1. Field of the Invention
This invention relates to a method for the production of a superplastic composite material comprising an aluminum metal substance such as 2124 aluminum alloy or 6061 aluminum alloy used as a matrix and silicon nitride whiskers or particles incorporated as a reinforcing agent in the matrix.
2. Prior Art Statement
The fiber-reinforced metal material (FRM), a composite material which comprises such a metallic matrix as aluminum or an aluminum alloy and whiskers or particles of SiC or Si.sub.3 N.sub.4, is light, exhibits high rigidity and strength, and excels in resistance to heat and resistance to friction and, therefore, is suitable as a material for structural members of automobile engine parts and of aerospace equipment.
Such relatively simple parts as automobile engine parts (pistons and connecting rods, for example) can be directly molded in their finished shaped by the melt forging method or powder metallurgy method using the aforementioned FRM in the form of melt or powder. Such intricately-shaped parts as aircraft door panels, for example, are produced by preparatorily producing a composite material plate from the melt or powder of FRM and forming the composite material plate in a desired shape. Thus these intricately-shaped parts require secondary fabrication. Among the techniques available for the secondary fabrication, hot precision machining is most practical. A need has arisen for developing a composite plate, a composite material plate of superplasticity, suitable for the hot precision machine.
The whiskers or particles of SiC or Si.sub.3 N.sub.4 (hereinafter referred to simply as "ceramic whiskers or particles") which are contained in the composite materials are extremely hard. The conventional composite materials using the ceramic whiskers or particles suffer from notable degradation of ductility (workability) when the content of such ceramic whiskers or particles reaches several percent. For example, a composite material containing ceramic whiskers or particles sustains defects due to the ceramic whiskers or particles when the composite material is machined.
For the superplastic composite material to retain its high rigidity and strength intact, it is necessary for the matrix and the ceramic whiskers or particles to be strongly joined at their boundary surface. For the composite material to manifest superplasticity, it is necessary for the matrix to be formed of very minute crystal grains.